GAS DIFFUSION LAYER FOR A FUEL CELL, AND FUEL CELL

Abstract

The invention relates to a gas diffusion layer (1) for a fuel cell (3), comprising a composite material (5) that contains electrically conducting particles (7), a binder and fibers (9), preferably carbon fibers, the particles (7) and the fibers (9) being present in the composite material (5) in the form of a mixture. The invention also relates to a fuel cell and to a method for producing the gas diffusion layer.

Claims

1. A gas diffusion layer (1) for a fuel cell (3), comprising a composite material (5) containing electrically conductive particles (7), a binder and fibers (9), wherein the particles (7) and the fibers (9) are present as a mixture in the composite material (5).

2. The gas diffusion layer (1) as claimed in claim 1, wherein the gas diffusion layer (1) has precisely one layer (11) and the one layer (11) comprises the composite material (.sup.5).

3. The gas diffusion layer (1) as claimed claim 1, wherein the fibers (9) have a length L (12) of at least 0.2 mm.

4. The gas diffusion layer (1) as claimed in claim 1, wherein the fibers (9) have a diameter Df of from 5 μm to 15 μm.

5. The gas diffusion layer (1) as claimed in claim 1, wherein the composite material (5) has elastic properties.

6. The gas diffusion layer (1) as claimed in claim 1, wherein the gas diffusion layer (1) has a thickness D (14) of from 10 μm to 300 μm.

7. The gas diffusion layer (1) as claimed in claim 1, wherein the composite material (5) contains from 1% by weight to 20% by weight of a first binder, from 0% by weight to 20% by weight of a second binder, from 1% by weight to 50% by weight of the fibers (9), from 0% by weight to 96% by weight of the electrically conductive particles (7) having an average diameter dm of from 0.5 μm to 50 μm and from 2% by weight to 98% by weight of the electrically conductive particles (7) having an average diameter dm of less than 0.5 μm.

8. A fuel cell (3) comprising a gas diffusion layer (1) as claimed in claim 1, wherein the fuel cell (3) is a polymer electrolyte fuel cell (PEMFC).

9. The fuel cell (3) as claimed in claim 8, wherein the fuel cell (3) comprises a gas distributor structure (16) having a surface (18) and the surface (18) has raised regions (20) for conducting gas and neighboring raised regions (20) are at a spacing A (22) from one another, where the length L (12) of the fibers (9) is at least twice as long as the spacing A (22).

10. A process for producing a gas diffusion layer (1) as claimed in claim 1, comprising the following steps: a. Production of a first mixture containing the first fiber, a solvent and an additive, b. Application of the first mixture to the electrically conductive particles (7) and the fibers (9) so as to form a second mixture, c. Compounding of the second mixture and extrusion or rolling-out of a film from the second mixture.

11. A gas diffusion layer (1) for a fuel cell (3), comprising a composite material (5) containing electrically conductive particles (7), a binder and carbon fibers (9), wherein the particles (7) and the fibers (9) are present as a mixture in the composite material (5).

12. The gas diffusion layer (1) as claimed claim 1, wherein the fibers (9) have a length L (12) of at least 2 mm.

13. The gas diffusion layer (1) as claimed claim 1, wherein the fibers (9) have a length L (12) of at least 2 mm and not more than 12 mm.

14. The gas diffusion layer (1) as claimed in claim 1, wherein the gas diffusion layer (1) has a thickness D (14) of from 20 μm to 150 μm.

15. The gas diffusion layer (1) as claimed in claim 1, wherein the composite material (5) contains from 2% by weight to 10% by weight of a first binder, which is polyvinylidene fluoride (PVDF), from 1% by weight to 10% by weight of a second binder, which is polytetrafluoroethylene (PTFE), from 5% by weight to 20% by weight of the fibers (9), from 10% by weight to 50% by weight of the electrically conductive particles (7) having an average diameter dm of from 0.5 μm to 50 μm and 10% by weight to 78% by weight of the electrically conductive particles (7) having an average diameter dm of less than 0.5 μm.

16. The fuel cell (3) as claimed in claim 8, wherein the fuel cell (3) comprises a gas distributor structure (16) having a surface (18) and the surface (18) has raised regions (20) for conducting gas and neighboring raised regions (20) are at a spacing A (22) from one another, where the length L (12) of the fibers (9) is at least three times as long and not more than fifty times as long as the spacing A (22).

17. A process for producing a gas diffusion layer (1) as claimed in claim 1, comprising the following steps: a. Production of a first mixture containing the first fiber, a solvent and an additive, b. Application of the first mixture to the electrically conductive particles (7) and the fibers (9) using a fluidized bed so as to form a second mixture, c. Compounding of the second mixture and extrusion or rolling-out of a film from the second mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the invention will be explained further with the aid of the drawings and the following description.

[0049] The drawings show:

[0050] FIG. 1 a fuel cell stack,

[0051] FIG. 2 a fuel cell having a gas diffusion layer according to the prior art and

[0052] FIG. 3 a fuel cell having a gas diffusion layer according to the invention.

DETAILED DESCRIPTION

[0053] In the following description of embodiments of the invention, identical or similar elements are denoted by identical reference numerals, with a repeated description of these elements in individual cases being dispensed with. The figures depict the subject matter of the invention only schematically.

[0054] FIG. 1 shows a schematic depiction of a fuel cell stack 4 comprising a plurality of fuel cells 3. Each fuel cell 3 comprises a membrane 24, two gas diffusion layers 1, an anode 30 and a cathode 32. The individual fuel cells 3 are separated from one another by bipolar plates 50, which can comprise a cooling plate 45.

[0055] The fuel cell stack 4, to which hydrogen 40 and oxygen 42 and also a cooling medium 44 are supplied, is closed off by two end plates 48 and has current collectors 52. The various feed conduits are separated from one another by seals 46.

[0056] FIG. 2 shows a schematic depiction of a fuel cell 3 which comprises a gas diffusion layer 1 according to the prior art.

[0057] The fuel cell 3 comprises a membrane 24 on both sides of which a catalyst layer 34 is arranged. Next to the catalyst layer 34, there is in each case a gas diffusion layer 1, which in each case is made up of a support structure 38 and a microporous layer 36, both on the side of the anode 30 and on the side of the cathode 32. The support structure 38 has a larger pore size than the microporous layer 36 and is arranged on the side of the gas diffusion layer 1 facing away from the membrane 24. The gas diffusion layers 1 are each enclosed by a gas distributor structure 16 through which hydrogen 40 or oxygen 42 is supplied to the gas diffusion layers 1. The gas distributor structures 16 have surfaces 18 having raised regions 20. The raised regions 20 are at a spacing A 22 from one another, as a result of which gas feed channels 26 are formed.

[0058] FIG. 3 shows a fuel cell 3 comprising a gas diffusion layer 1 according to the invention. The fuel cell 3 corresponds substantially to the fuel cell 3 depicted in FIG. 2, with the difference that in FIG. 3 the gas diffusion layers 1 are configured according to the invention. The gas diffusion layers 1 consist of only one layer 11 which extends from the catalyst layer 34 to the surface 18 of the gas distributor structure 16. The gas diffusion layers 1 are made up of a composite material 5 which contains electrically conductive particles 7 and fibers 9. The fibers 9 have a length L 12 which is at least twice as long as the spacing A 22 between the raised regions 20 of the gas distributor structures 16. Furthermore, the gas diffusion layers 1 have a thickness D 14.

[0059] The gas diffusion layers 1 as shown in FIG. 3, which are made up of the composite material 5, replace in each case the support structures 38 and the microporous layers 36 which are depicted in FIG. 2.

[0060] The invention is not restricted to the working examples described here and the aspects emphasized therein. Rather, many modifications which are of the kind that a person skilled in the art would routinely make are possible within the scope defined by the claims.